It is known that when a beam of electromagnetic radiation is caused to impinge on the surface of a sample at an oblique or normal angle, reflected electromagnetic radiation from said sample generally contains components not only from its surface, but also from the backside thereof. The effect of said backside reflections can be difficult to model, and makes characterization of surface films far more difficult, even essentially impossible. It is therefore desirable to reduce or eliminate the presence of said backside reflections. It is disclosed that the identified problem can present in systems where a sample is elongated such as a ribbon or sheet, and is continuously pulled over the means for supporting a sample. Where said sample and means for supporting it have different refractive indicies, back side reflections develop.
Known Patents relevant to Backside Reflections are:                Patent to He et al., U.S. Pat. No. 5,963,327;        Patent to Johs, U.S. Pat. No. 5,929,993;        Patent to Synowicki, U.S. Pat. No. 6,738,139;        Patent to Johs et al. U.S. Pat. No. 5,936,734;        Patent to Herzinger et al. U.S. Pat. No. 6,455,853.Other Patents and Published Applications which were cited in Parent application Ser. No. 11/452,483 are:        U.S. Pat. No. 5,917,594;        U.S. Pat. No. 6,323,946;        U.S. Pat. No. 6,583,877;        U.S. Pat. No. 5,608,526;        U.S. Pat. No. 5,910,842;        U.S. Pat. No. 6,734,967;        Patent Application No. US 2002/030813;        Patent Application No. US 2004/008349;        Patent Application No. US 2004/100632;        Patent Application No. US 2005/105090.        
Need remains for systems which reduce the effect of reflections for the backside of a sample when electromagnetic radiation is caused to impinge on a front side thereof at an oblique or normal angle of incidence.